Largest N.B. measles outbreak in decades pushing Canada's case count to 5-year high

A measles outbreak in New Brunswick is set to push Canada's annual case count to the highest it's been in five years, highlighting how infectious the disease is and how low vaccination rates have allowed it to take hold, says an immunologist.

Forty-four cases have now been confirmed in the province, all in health Zone 3, which includes Fredericton and parts of the Upper Saint John River Valley area, the Department of Health said late Wednesday.

It's the largest outbreak New Brunswick has on record in "several decades," said spokesperson David Kelly. The most recent outbreak was in 2019, when Zone 2, the Saint John region, saw a total of 12 cases over two months.

Asked how confident the department is that it will be able to keep the current outbreak under control, Kelly said in an emailed statement, "Public Health continues to closely monitor the situation and will inform the public if any new exposures occur."

All of the cases can be traced back to the initial one reported Oct. 24, involving a person who recently travelled internationally, but not all of them were necessarily in direct contact, as more spread would have occurred, he said.

They were all considered vulnerable because they either never had measles before, were unvaccinated or immunocompromised, said Kelly. Anyone born in 1970 or after who has not had two doses of measles vaccine and has never had measles is considered at risk, he noted.

More than 80 per cent of the infected people are 19 years old or under. Kelly dd not provide a further breakdown, or the age of the the youngest case.

At least three people required hospitalization, but have since been discharged.

The New Brunswick outbreak, declared on Nov. 1, is part of a national surge, which reached 100 cases as of Nov. 2, and resulted in the death of child under five in Hamilton, according to the Public Health Agency of Canada.

The last time the country saw more cases was in 2019, when 103 cases were confirmed.

New Brunswick is doing the heavy lifting, which is "unusual in some ways because often we've seen measles outbreaks in large urban centres," said Dawn Bowdish, an immunologist and professor of medicine at McMaster University in Hamilton.

"But this just speaks to the fact that measles, once it gets into a population, can spread really, really quickly, and we have more vulnerable children than we've had in decades in Canada," she said.

Measles is the most infectious respiratory infection experts know of, said Bowdish, citing an investigation that found when an infected child got off a plane at an airport, an unvaccinated person three gates down got sick. "So that's just how contagious it is."

The virus is transmitted through the air or by direct contact with nasal or throat secretions of an infected person.